The invention relates to an adjusting device for changing the angle of rotation of a camshaft relative to the crankshaft of an internal-combustion engine.
To guarantee reliable engine startup in an internal-combustion engine with a hydraulic or electric camshaft adjuster, the camshaft must be located in a certain base position relative to the crankshaft during startup. Typically, for an inlet camshaft, it is a “retarded” position, and for an exhaust camshaft, it is an “advanced” position.
In normal vehicle operation, the camshaft is moved in a controlled way into the appropriate base position when the engine is turned off and the camshaft is fixed or locked in this position. For this purpose, the electric camshaft adjustment uses an electric adjusting motor and the hydraulic camshaft adjustment uses a hydraulic rotary piston adjuster, which has vane cells, pivoting vanes, or segmented vanes as a locking unit. This unit fixes the hydraulic adjuster in its base position until a sufficiently high oil pressure has been established for adjusting the camshaft after the restart of the internal-combustion engine.
However, if the internal-combustion engine stalls, a controlled adjustment of the hydraulic camshaft adjuster is impossible, so that the camshaft can be in an undefined position outside of the base position.
For hydraulic camshaft adjusters with a “retarded” base position, when the internal-combustion engine is next started and there is insufficient oil pressure due to the camshaft friction torque, which acts against the camshaft direction of rotation, the camshaft is automatically adjusted into the retarded base position. If the base position is an “advanced” position, for insufficient oil pressure the camshaft must be adjusted against the camshaft friction torque into the advanced position. This is usually performed with the help of a compensating spring, which generates a torque that is equal but opposite the camshaft friction torque.
These methods typical for hydraulic camshaft adjusters for reaching the base position after the internal-combustion engine has stalled are not required for electrically driven camshaft adjusters, because the adjusting motor can adjust the camshaft into the appropriate base position even for a stopped internal-combustion engine or during startup. However, for electric camshaft adjusters, power to the adjusting motor and/or its controller can be lost and therefore the base or emergency running position cannot be reached, which is necessary for at least limited operation and restart.
In DE 41 10 195 A1, an electric adjusting device that adjusts an angle of rotation of the camshaft relative to the crankshaft of an internal-combustion engine is described, with an adjusting gear unit, which is embodied as a triple-shaft gear system, and an input part that is fixed to the crankshaft, an output part that is fixed to the camshaft, as well as an adjusting shaft. Here, the adjusting shaft is connected in a torsion-proof manner to an electric adjusting motor, which has a permanent magnet motor and a stator that is fixed to the housing, wherein for a stationary adjusting shaft, between the input and output part there is a stationary gear ratio
      i    0    =            Output      ⁢                          ⁢      tooth      ⁢                          ⁢      number      ⁢                          ⁢              Z        NW                    Input      ⁢                          ⁢      tooth      ⁢                          ⁢      number      ⁢                          ⁢              Z        KW            whose magnitude determines the type of gear type (positive or negative gear) and the adjusting direction of the camshaft (advanced or retarded base position). This adjusting device strives for a smooth and precise setting of the camshaft position. So that the function of the internal-combustion engine can be maintained at least to some extent if the adjusting-motor system breaks down, there is a limit on the adjusting angle. However, a reference to reaching the base position or an emergency running position in such a case is lacking.